An all-digital phase-locked loop (PLL) circuit in which resolution in the phase detector and digitally controlled oscillator (DCO) exactly matches the gate-delay time is presented. The pulse delay circuit is connected in a ring shape with 32 inverters (2 5 inverters). With the inverter gate-delay time as the time base, the pulse phase difference is detected simultaneously with the generation of the output clock. In this system, the phase detector and oscillator share a single ring-delay-line (RDL). This means the resolution is the same at all times, making a high-speed response possible. In a prototype integrated circuit (IC) using a 0.65-m CMOS, the generation of a frequency multiplication clock was achieved with four reference clocks, and that of a phase-locked clock with seven reference clocks, for a high-speed response. The cell size was 1.08 1.08 mm 2 , and the output clock frequency had a wide range of 50 kHz 60 MHz. The multiplication range of the clock frequency was also a very wide 4 1022, and a high level of precision was achieved with a clock jitter standard deviation of 234 ps. This digital PLL can withstand a broad range of operating environments, from 30 C 140 C, and is suitable for making a programmable clock generator on a chip.
For achieving an all-digital resonant MEMS gyroscope, this paper presents an all-digital MEMS tuning-fork self-excited vibration control method, using TAD (Time-A/D converter)-based all-digital PLL (TAD-ADPLL) by applying a unique control algorithm based on entirely time-domain processing, which uses no conventional analog method such as automatic gain control (AGC) or automatic level control (ALC). The proposed algorithm involves three-step processing: 1) driving a tuning-fork using the ADPLL for searching its selfresonant frequency, 2) comparing the phase difference between drive-pulse signal and monitor-pulse signal, which should be 90º (π/2-radian) each other, and 3) keeping 90º-relationship between them even with any drift factors such as temperature, supply voltage, etc. In this method, TAD-type TDC (time-to-digital converter) digitizes the resonant frequency and phase difference alternately in order to realize self-excited vibration condition along with TAD-type DCO (digitally-controlled oscillator) without the need for any analog circuit method. By using a conventional piezoelectric MEMS tuning-fork element, we experimentally confirmed its self-excited vibration, resulting in its resonance jitter level of σ = 52.6ns at 37µs-self-resonance period. Finally, we propose an all-digital synchronous detection of angular-rate signal for achieving a digital-type gyro sensor.
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